Types Of Waste Materials Research Articles

Simultaneous separation of Fe & Al and extraction of Fe from waste coal fly ash: Altering the charge sequence of ions by electrolysis.

A significant amount of coal fly ash is generated and this type of waste material causes severe environmental hazards. Metal (Al and Fe) extraction from coal fly ash is beneficial to the resource utilization of waste coal fly ash. However, the coexistence of Al and Fe in coal fly ash means that the separation of Al and Fe is required, which is a key and difficult step to prepare high value-added products from coal fly ash. This work presents a novel electrolysis method to alter the charge sequence of Al3+, Fe3+, and H2O, leading to a process different from their natural tendency for simultaneous separation of Fe3+ and Al3+, and extraction of Fe. The single iron removal efficiency was 43.48%, and the aluminum extraction efficiency was <0.30% under optimal conditions. The iron product had a purity of 98.3wt% Fe, 0.45wt% Al, and 0.18wt% S. This process occurs without chemical additions and expensive membranes, avoiding impurity introduction, slag generation, and membrane limitations. Fe(s), H2(g), Al2(SO4)3(aq), and O2(g) are the main products during the electrolysis. Flake Fe is selectively produced instead of colloidal Fe(OH)3. Fe is a magnetic substance and is easier to remove from the solution by magnets than colloidal Fe(OH)3. H2 is a green fuel. Wastewater (Al2(SO4)3(aq)) can be directly used to further extract alumina. Therefore, this study provides an alternative method of zero pollution discharge for simultaneous separation of Fe3+ and Al3+, and extraction of Fe from coal fly ash leachate.

Mixture Optimization of Concrete Paving Blocks Containing Waste Silt

Most of the waste materials recycled for the production of new construction materials are by-products of various manufacturing processes, such as the aggregate washing process. Recycling such materials is of paramount importance since it could reduce the adverse environmental impacts resulting from landfilling. Various studies have attempted to recycle different types of waste materials and by-products into concrete paving blocks. However, the availability of literature on concrete paving blocks containing waste silt is quite scarce. Thus, the current paper focuses on mix design optimization and production of concrete paving blocks containing high amounts of waste silt resulting from the aggregate production process. Using the mixture Design of Experiments (DOE), 12 sets of concrete paving blocks with different aggregate blends were produced to optimize the mix design. Once the final mix design was achieved, the physical and mechanical properties of the concrete paving blocks were investigated following the EN 1338 standard. Shape and dimension measurements and various tests, including water absorption, tensile splitting strength, abrasion resistance, and slip/skid resistance were conducted on the experimental concrete paving samples. Overall, the produced concrete paving blocks showed promising properties for future applications in pedestrian walking paths.

Recycling of Waste Materials Using Bitumen Emulsion for Road Pavement Stabilized Base Courses: a Laboratory Investigation

The valorisation and reuse of waste materials can enhance the environmental sustainability of road constructions, especially by means of cold recycling techniques, which, moreover, allow to reduce polluting emissions in atmosphere. Among the various technological approaches, the use of bitumen emulsion to stabilize waste materials is very common, especially in case of reclaimed asphalt pavement (RAP) aggregates. However, even other types of waste materials could be considered using a Cold Central Plant Recycling (CCPR) approach. The paper discusses the main results of a laboratory investigation aimed to evaluate the mechanical performance of bitumen emulsion stabilized mixtures for road pavements base courses, prepared with RAP, steel slag, coal ash and glass wastes, used with various percentages. In a first step of the laboratory study, both physical and toxicological properties of each waste material have been investigated, in order to assess their environmental compatibility. Subsequently, an extensive mechanical analysis of the bitumen emulsion stabilized mixtures has been carried out in the laboratory, in terms of indirect tensile strength, indirect tensile stiffness modulus at three temperatures (10°C, 25°C, 40°C) and repeated load axial tests at 30°C. The moisture resistance of the mixes has been also investigated by means of indirect tensile strength tests carried out on soaked specimens. Very good results have been observed, depending on the mix composition: indirect tensile strength at 25 °C on dry specimens up to 0.52 MPa and stiffness modulus up to 4,056 MPa (at 25 °C, for a rise time equal to 124 ms). Therefore, it has been verified that the waste materials considered in the study can be successfully reused to completely substitute conventional aggregates in bitumen emulsion stabilized mixtures for road pavements base courses.

A Review of Hazardous Compounds Present in Construction Waste Materials

Construction industry around the world is well-known as a massive contributor of waste materials and environmental impacts. Among the types of waste materials generated by this industry are concrete, plastic, wood, ceramic, and asbestos. These waste materials, in general, are chemically fused through various manufacturing processes before being transported for the construction usage. Addition of chemical compounds such as arsenic, copper, cyanide, nickel, chromium, lead, sulphate, and zinc are mainly for enhancing the mechanical and physical properties of the materials so that the materials could last longer, perform well and withstand external forces. However, construction materials that are made up of these chemical compounds are threatening the nature and human beings once the materials are used up and the leftover from the construction industry are thrown away without proper waste management practice. The aim of the study was to review hazardous compounds presented in construction waste materials and suggest ways to manage it effectively. The methodology is literature review, data collection from published articles, and data analysis. Findings from this study showed that concrete, plastic, wood, ceramic, and asbestos are among the waste materials that are made up of hazardous compounds, which impact the environment and mankind living today. As a mitigation measure, a proper waste management practice is necessary among the construction practitioners to protect humans and biological factors, save some landfill spaces, preserve some natural resources, prevent soil and underground water channel contamination, avoiding illegal dumping activities, and promotes sustainability factors. Obeying the enforced rules and regulations, utilisation of various waste management technologies, on-site waste segregation and proper storage, waste substitutions, and making use of well-structured framework developed by researchers and construction consultancy are among the methods that can be adopted in polishing the current waste management practice.

Alkali-Activated Mortars with Recycled Fines and Hemp as a Sand.

Nowadays, effective and eco-friendly ways of using waste materials that could replace natural resources (for example, sand) in the production of concrete composites are highly sought. The article presents the results of research on geopolymer composites produced from two types of waste materials—hemp and fine fractions recovered from recycled cement concrete, which were both used as a replacement for standard sand. A total of two research experiments were conducted. In the first experiment, geopolymer mortars were made using the standard sand, which was substituted with recycled fines, from 0% to 30% by weight. In the second study, geopolymers containing organic filler were designed, where the variables were (i) the amount of hemp and the percent of sand by volume (0%, 2.5%, and 5%) and(ii) the amount of hydrated lime and the percent of fly ash (by weight) (0%, 2%, and 4%) that were prepared. In both cases, the basic properties of the prepared composites were determined, including their flexural strength, compressive strength, volume density in a dry and saturated state, and water absorption by weight. Observations of the microstructure of the geopolymers using an electron and optical microscope were also conducted. The test results show that both materials (hemp and recycled fines) and the appropriate selection of the proportions of mortar components and can produce composites with better physical and mechanical properties compared to mortars made of only natural sand. The detailed results show that recycled fines (RF) can be a valuable substitute for natural sand. The presence of 30% recycled fines (by weight) as a replacement for natural sand in the alkali-activated mortar increased its compressive strength by 26% and its flexural strength by 9% compared to control composites (compared to composites made entirely of sand without its alternatives). The good dispersion of both materials in the geopolymer matrix probably contributed to filling of the pores and reducing the water absorption of the composites. The use of hemp as a sand substitute generally caused a decrease in the strength properties of geopolymer mortar, but satisfactory results were achieved with the substitution of 2.5% hemp (by volume) as a replacement for standard sand (40 MPa for compressive strength, and 6.3MPa for flexural strength). Both of these waste materials could be used as a substitute for natural sand and are examples of an eco-friendly and sustainable substitution to save natural, non-renewable resources.

Comprehensive review study for the effect of utilizing waste ma-terials on the thermal conductivity of concretes

Since concrete is one of the most popularly utilized building mixtures in construction, a high demand of natural resources is significantly emerged. Therefore, a skyrocketed attention has been paid to create new opportunities for the use of recycle materials to develop a new construc-tion substance with more satisfactory properties. The use of waste products in concrete is not only economical, but it helps in solid waste management as well. Among various properties of concrete, thermal conductivity is a crucial factor that plays an important role in in building insu-lation by evaluating a material's capacity to transfer heat. This paper aims to review the potential application of waste materials in concrete as additive ingredients and investigate the effect of this waste material on thermal conductivity of concrete. The review of literature revealed that the application of most of the waste materials exhibited an obvious potential as thermal insulator. However, further investigated work is needed to highlight the advantages of utilizing waste mate-rials in concrete containing various type of waste materials

Mechanical properties of stone mastic asphalt containing high-density polyethene: An Australian case

Using stone mastic asphalt (SMA) has increased considerably, mostly due to the improvement in serviceability of pavements. This type of asphalt mix is made with more coarse aggregates than fine aggregates. Therefore, using proper bitumen with a better coating among the aggregates is important. On the other hand, since the population grows, the production of waste materials drastically increases. Therefore, the importance of using recycled materials in other industries has increased every day. One of the most prominent types of waste materials is high-density polyethene (HDPE). HDPE is polymer waste and can improve the performance of bitumen. HDPE can be found in many municipal wastes, such as plastic bottles. Therefore, constructing pavements containing HDPE can reduce waste materials and the cost of maintaining and rehabilitating roads from the improvements of mechanical properties and performances of mixtures. This study aimed to investigate the effectiveness of HDPE on the mechanical properties and performance of SMA. Hence, Marshall properties, maximum density, bulk density, and stability were measured for the mechanical properties. Wheel tracking and four-point bending test were carried out as the performance evaluation of rutting and fatigue resistance, respectively. The results showed SMA mixtures containing 4% HDPE had the best fatigue resistance, while rutting performance was 8% HDPE. The maximum fatigue life and minimum rutting depth were recorded as 157,090 cycles and 1.05 mm, respectively.

Degradations of endocrine-disrupting chemicals and pharmaceutical compounds in wastewater with carbon-based nanomaterials: a critical review

Although water occupies 75% of the earth's surface, only 0.0067% of the total water is available for human activities. These statistics further decline with the population growth and consequent multiplication in the amount of annual waste produced. The demand for clean and safe drinking water has always been a prime concern in the global scenario. Among various types of waste materials, endocrine-disrupting chemicals (EDCs) and pharmaceutical effluents have become a constant threat to the aquatic ecosystem and possess challenges worldwide. Endocrine-disrupting chemicals (EDCs) are a mixed group of emerging concern chemicals with the ability to mimic the mechanisms of biosynthesis, transport, and metabolism of hormones. These chemicals pose various health threats such as early puberty, infertility, obesity, diabetes, reproductive disorders, cancerous tumors, and related disorders (immune cells, hormones' activity, and various organs). On the other hand, pharmaceutical compounds such as antibiotics also harm the natural environment, human health, and soil microbiology. Their low concentration, ranging from a few ng/L to μg/L, gives rise to a micro-pollution phenomenon, which makes it difficult to detect, analyze, and degrade in wastewater treatment plants. Activated carbons (ACs) and other adsorbents, including naturally occurring materials (wood, keratin) are considered as nanomaterials (NMs) reference for the separation of organic pollutants. It is generally acknowledged that mass-transfer phenomena control sorption kinetics at the liquid/solid interface, with retention controlled by the sorbent/sorbate properties. Therefore, the type of interaction (strong or weak van der Waals forces) and the hydrophilic/hydrophobic properties of the adsorbent are two crucial factors. Besides, EDCs and pharmaceutical compound sorption on such kinds of nanoporous solids depend on both the molecule size and charge density. The applications of nanomaterials on non-conservative methods, like advanced oxidation processes or AOPs (e.g., photocatalysis and Fenton reaction), are contemplated as more apt in comparison to conservative technology like reverse osmosis nanofiltration, and adsorption, etc. One of the reasons is that AOPs generate free radicals (hydroxyls), which are strong oxidants for the demineralization of organic compounds and the extreme case that hydroxyl radicals can attack any kinds of pollutants with the generation of only water and carbon dioxide as final products. AOPs may imply the use of NMs as either catalysts or photocatalysts, which improve the selective removal of the target pollutant. Therefore, various literature reviews have revealed that there is a timely need to upgrade the efficiency of the remediation approaches to protect the environment against EDCs and pharmaceuticals adequately. There is currently a lack of definitive risk assessment tools due to their complicated detection and associated insufficiency in the health risk database. Hence, our present review focuses on applying carbon-based nanomaterials to remove EDCs and pharmaceuticals from aqueous systems. The paper covers the effect of these pollutants and photocatalytic methods for treating these compounds in wastewater, along with their limitations and challenges, plausible solutions, and prospects of such techniques.

Dynamic and Analysis of A Geo-Polymer Concrete Structure

The standard portland cement (OPC) was traditionally used as the binding agent in concrete. However it is also important to find alternative emissions-free concrete binding agents to reduce environmental damage caused by cement manufacturing. Geopolymers, also known as inorganic polymers, use byproducts like fly ash rather than cement. Recent studies have shown that geopolymer concrete based on fly ash has enough properties for use. As the geopolymer strength mechanism is different from the OPC binder, an appropriate constituent model for geopolymer concrete must be obtained in order to predict the load-deflection behavior and strength of geopolymer concrete structural components. A number of problems faced with today's cement industry are addressed by geopolymer binders. These binders have similar or better engineering qualities in comparison with cement and can use many types of waste materials.&#x0D; This project describes the seismic analysis of buildings with high-rise structures, the model of residential G+10 buildings with traditional concrete and geopolymer concrete properties is modelled and analysis is carried out using the response spectra method considering the position of the building in zone III, this analysis would generate the effect of higher vibration modes and real force distribution in elastic range. Test results include maximum story shifts, maximum story drifts, story shears and story stiffness, and an efficient lateral load resistance system, helping to establish whether geo-polymer concrete can be used in high-rise building construction as dynamic loads are included in the high-rise structures&#x0D;

Discernment of synergy during the co‐pyrolysis of lipid‐extracted microalgae and digested municipal solid waste: a thermogravimetric–mass spectrometric study

AbstractBACKGROUNDThe current study investigated the co‐pyrolysis nature of biomasses, gas yields, kinetics and thermodynamics of Chroococcus sp. (CC), digested municipal solid waste (DMSW) and their mixtures using thermogravimetric analysis and mass spectrometry.RESULTSThermogravimetric/differential thermogravimetric analysis indicated three major weight loss stages: dehydration (50–150 °C), thermal degradation of structural components (150–550 °C) and char decomposition (550–800 °C). The gases released during the process mainly contained CO, CH4, CO2 and H2 as main components. Also, with an increase in the composition of CC, the hydrogen yields were noticed to increase. Model‐free isoconversional methods, the Kissinger–Akahira–Sunose and Friedman methods, were considered to identify the activation energy. The kinetic results showed that an increase in the percentage of CC in the mixture lowered the activation energy. The activation energies recorded for CC, DMSW, CD‐1, ‐2 and ‐3 were 282.11, 202.55, 210.54, 145.46 and 139.98 kJ mol−1, respectively.CONCLUSIONSThermodynamic and kinetic analysis for CC, DMSW and their mixtures can be effectively used for reactor design and process optimization for similar types of waste materials. © 2021 Society of Chemical Industry (SCI).

Disposal of wooden wastes used as heavy metal adsorbents as components of building bricks

The recovery of wastes is the basis of the Circular Economy. In recent years, there is an increased interest in the use of agro-industrial wastes as simple and “low-cost” adsorbents in the removal of heavy metals from wastewaters. However, the fate or reuse of such adsorbents saturated with pollutants has not been discussed deeply. The novelty of this paper is the valorization of pine sawdust waste and pine sawdust char, previously used as adsorbents for Ni(II), Zn(II), Cd(II) and their mixture, in the manufacture of porous fired clay bricks, which are an important kind of bricks due to their low weight and low thermal conductivity. Initially, both residues were evaluated as potential adsorbents for the heavy metals under study. The obtained results were much better for biochar with adsorption efficiencies close to 100%, both in individual and mixed systems, the later closer to real wastewater cases. Finally, 20% by volume of the contaminated biomass waste was incorporated into ceramic matrices, increasing the apparent porosity with respect to a brick of reference. The evaluation of the physical properties and their mechanical characterization, determined a decrease in the quality of these bricks even still within the current regulations for construction purposes. The s-s curves showed differences in the mechanical behavior associated with the type of waste material, being those obtained for bricks with biochar similar to those of the bricks of reference. Heavy metals immobilized in the clay matrix did not introduce significant changes in the physical and mechanical properties checked. Therefore, it is possible to take advantage of wood waste used as heavy metal adsorbents in wastewater treatment, with an option for its proper disposal.

Microstructure and X-Ray Diffraction Analysis of Aluminum-Fly Ash Composites Produced by Compocasting Method

Abstract Industrial and agro-wastes, such as fly ash, red mud, and rice husk ash, have become tremendous materials to be used as reinforcement in composite materials. In addition, these materials have potential to replace conventional ceramic reinforcement materials, such as aluminum oxide (Al2O3) and silicon carbide (SiC), as they can produce better composite materials with excellent properties and reduce the cost of production. Among the various types of waste materials used, fly ash has gained the widespread attention of researchers in aluminum matrix composite (AMC) production as reinforcement to enhance the properties of AMCs and reduce the production cost. In this research, LM6 (aluminum-silicon) alloy was reinforced with different amounts (4, 5, and 6 wt. %) of fly ash. These various compositions of LM6 reinforced with fly ash composites (AMCs) were fabricated by a compocasting method. The AMCs were then characterized based on microstructural (morphology, shape and size of the structure, and structure of existing elements) and phase analysis by scanning electron microscopy (SEM) and X-ray diffraction pattern (XRD). The existence of fly ash particles and some intermetallic compounds, such as Al2O3, silicon oxide, aluminum silicate, aluminum silicon, and calcium silicide, in the fabricated AMCs were confirmed through an XRD pattern. The SEM micrograph revealed that the microstructure of fabricated AMCs was refined with the incorporation of fly ash particles. The size of silicon phases decreased from 50 (unreinforced LM6) to 2.12 μm (LM6 fly ash composite with 6 wt. % of fly ash). Hence, it is found that the incorporation of fly ash particles is able to enhance the microstructure of fabricated AMCs.

The Effect of Palm Oil Fuel Clinker Powder and Cockleshell Powder as Cement Replacement on Durability Properties of the Concrete Mortar

The concepts of eco-friendly building are getting more attention today. The standard materials of concrete that used such as cement and aggregate are not totally environmentally friendly. Thus, many materials from natural sources can be an alternative to the realization of the green building concept. As a result, many researchers have devoted their attention towards identifying eco-friendlier substitutions to be used in concrete. This study was conducted to investigate the efficiency of two different types of waste materials which are palm oil clinker (POC) and cockle shell (CS) as partial replacement of cement on durability aspects. The POC and CS materials were ground to achieve a small particle size to fit with the concrete mix as cement replacement. The replacement of cement was at different levels (10% and 20%). Six mix proportions were made with different percentage of palm oil clinker powder POCP and cockle shell powder CSP. The specimens were cured by immersing in water for 7 and 28 days. The tests that were conducted were acid resistance test and water absorption test. Therefore, the experiment result showed that the POC had a negative impact to the concrete in both tests while the CSP proved it is resistance to acid.

Bio-Mineralization process on concrete substituted with different types of waste materials

Million tons of waste materials were produced in the world each year and most of it is not recyclable. To protect the environment from pollution and depletion, it is imperative to find explication for the safe disposal of waste materials. Using waste material in concrete production is a propitious method for eliminating the waste and reducing the cost of concrete. Also, the green concrete technology is expanding, it is necessary to utilize wastes in concrete that is generated from all the sectors. In construction large amounts of concrete from buildings was generated and demolitions made up 30-40 % of total wastes. Around 33 tons of Copper slag is produced across the world and 6 to 6.5 tons in India. Electronic waste is emerging as a serious public health and environmental issue in India and approximately 2 million tons of e-waste is generated annually. Concrete produced from wastes will have declination over the strength and it is necessary to improve the properties by some other technique. Self-healing concrete is a brand-new technology that ‘heals’ its own cracks and indicates a promising future in reducing the inevitable deterioration of concrete structures and the high maintenance costs involved. This research includes the inclusion of waste materials into the concrete and determination of compressive Strength of waste substituted concrete. Three major Wastes such as Demolition Wastes, Copper slag and E-Wastes were chosen to replace for aggregate and Bacteria subtilis a spore forming bacteria was used as an admixture to improve the properties of concrete. From the results obtained it has been observed that self-healing technology proves to be the fruitful and considerable increase in mechanical properties.

Assessment of the properties of bricks made from stone dust and molten plastic for building and pedestrian pavement

The importance of bricks and the need to conserve the environment has led to the use of different types of waste material to replace either cement, clay or sand in the production of bricks. This study has looked into the use of molten plastic to replace Cement in sandcrete bricks. Molten plastic was mixed with stone dust at ratio 1:1, 1:2, 1:3 and 1:4 by weight. Each sample was designated as P1, P2, P3 and P4 respectively. The brick samples were subjected to mechanical and water absorption tests. An investigation was conducted on the bricks microstructures. Results showed that sample P1 is good for building, facial bricks, pedestrian and light traffic pavement under moderate weathering conditions according to ASTM C67, while sample P2 is okay for building bricks only under non-severe weathering condition. The remaining two bricks samples did not perform well under any conditions. The microstructural analysis revealed the effects of micro-voids sizes on the properties of the bricks

Effect of different types of waste materials used between double glazing box to isolate fatigue test machine noise

This study examines air, recycled plastic grains, fibers from rubber shreds and sawdust fibers as sound insulation materials to attenuate sound produced from continuous working lab fatigue test machine. These waste materials are filled in between a double glazed-aluminum framed box. The sound attenuation is tested at three studied 0.5, 1.0 and 1.5 m distances. Since the sound wave is propagated in three dimensions, the experimental work is employed in four upper, fronts, motor and sample fixture side directions. Moreover, the study is extended to examine temperature increase due to enclosing. Tests of sound level are carried out with closed and opened inlet and outlet designed slotting according to a box size. Gradual sound attenuation reaches 18, 20, 22 and 25% for air, plastic grains, rubber and sawdust fibers, respectively. The present work proves that waste materials are efficient in noise removal from sound sources. Also, they help the environment cleanliness from synthetic disposable bottles and tires as well as bio-wood wastes and assist the sustainability of earth.

Garbage Waste Segregation Using Deep Learning Techniques

Waste segregation is one of the primary challenges to recycling systems in major cities in our country. In India, 62 million tons of garbage is generated annually. Of this 5.6 million tons of wastes consist of plastic materials. About 60 percent of this is recycled every year. In addition, 11.9 million tons are recycled from 43 million tons of solid waste produced. Though the numbers sound good, a serious problem in the recycling industry is the segregation of waste before recycling or any other waste treatment processes. In India, at present situation waste is not segregated when collected from households. So a lot of workforce and effort are needed to separate this waste. In addition to this people working in this industry are prone to various infections caused due to toxic materials present in the waste. So the idea is to decrease the human intervention and make this waste segregation process more productive. The proposed work is aimed to build an image classifier that identifies the object and detects the type of waste material using Convolutional Neural Network. In this work, four different models of the CNN, such as ResNet50, DenseNet169, VGG16, and AlexNet, trained on ImageNet, are used to extract features from images and feed them into a classifier to make predictions and distinguish a type of waste from its corresponding category. The experimental results showed that the performance of DenseNet169 was significantly greater than all four models and the performance of ResNet50 is closer to DenseNet169.

An investigational study on properties of concrete produced with industrial waste red mud

Abstract The requirements for leading a proficient life is challenging for the rapid development of industries and they partially fulfil their tasks since many factors are not overcome by them successfully and one of that is safe disposal and utilization of waste generating at the end. All countries produces an enormous amount of different types of waste materials as by products from different sectors like industrial, agricultural etc. These waste materials if not deposited safely it may be hazardous. Also it is seen that for manufacturing of cement required huge amount of energy, causes releasing of huge CO2 in atmosphere resulting formation of environmental problems. So it is very important to use of industrial waste in construction industry especially for replacement of the cement in some proportion. Intension of this study is to inspect the performance of concrete by substituting cement by red mud. In this work, cement was partly replaced by red mud (RM) in different percentages (0%, 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18% and 20%), with 0.44 water cement (W.C) ratio with reference of Indian standard (IS) 10262:2019 guidelines, M30 grade concrete were prepared. Flow properties and strength properties like flexural, compressive, split tensile strength and chloride permeability tests were tested for 28 days on concrete with various mix proportions and test results were correlate with results of reference concrete. The study reveals that, partly replacing of 12% factory cement by red mud (RM) yields maximum strength, superior chloride permeability with better micro structure than conventional concrete.

Hydrometallurgical processes for heavy metals recovery from industrial sludges

Hydrometallurgical approaches have been successfully employed for metal separation and recovery from various types of waste materials. Therefore, hydrometallurgy is a promising technology for metal recovery and the removal of potentially toxic heavy metals found in industrial sludge. However, a comprehensive review that focuses on the heavy metal recovery from industrial sludge using hydrometallurgical approaches has not been conducted in the recent past. The present review discusses the capacity of hydrometallurgical techniques in recovering heavy metals sourced from different types of industrial sludges, highlighting recent scientific findings. Hydrometallurgical approaches primarily consist of three process stages: metal dissolution, concentration and purification, and metal recovery. The chemical characteristics of industrial sludge, including the type, concentration and speciation of heavy metals, directly impact selection of the best recovery method. Solvent extraction, ion-exchange, and adsorption are the major techniques employed in concentration and purification, whereas electrodeposition and precipitation are the main methods used in metals recovery. Future research should focus on the development of more efficient and environmentally-friendly methods for metal dissolution from industrial sludges contaminated with multiple metals, while increasing selectivity and energy use efficiency in the concentration and purification, and recovery steps.

Mechanical Properties of Normal Strength Concrete Containing Different Types of Waste Material as Coarse Aggregate Replacement

In this study, the effect of different types of waste materials on the mechanical properties of normal strength concrete was investigated. Three types of waste material crumbed rubber, granular plastic, and crushed brick with different percentage up to 15% ( by weight of coarse aggregate) were used. The effect of waste material on the compressive strength, splitting tensile strength, and static elastic modulus of hardened concrete for 28 days of curing with constant w/c= 0.45 were studied. The maximum loss in concrete compressive strength was recorded to be 54.95%, 50.31%, and 20.41% for concrete mix with 15% crumbed rubber and plastic aggregate and 5% crushed brick particles. Maximum reduction in splitting tensile strength noticed to be 65%, 43.15%, and 13.59% for 15% replacement of crumbed rubber, granular plastic, and crushed brick respectively. The maximum loss in static elastic modulus was found to be 48.29%, 27.14, and 11.23% for concrete mix with 15% crumbed rubber, granular plastic, and 5% crushed brick. From test results it is concluded that up to 15% waste material can be safely used to produce this type of recycled concrete.